Ecosystems

Question 1

What is an ecosystem?

Answer 1

A set of interacting, interdependent biotic and abiotic components

Question 2

What 2 types of factors can affect an ecosystem?

Answer 2

1- Biotic

2- Abiotic

Question 3

What is a biotic factor?

Answer 3

A living factor

Question 4

What is an abiotic factor?

Answer 4

A non-living factor

Question 5

Name 5 abiotic factors

Answer 5

1- Light
2- Temperature
3- Water availability
4- Oxygen availability
5- Edaphic soil factors

Question 6

Name 3 biotic factors

Answer 6

Competition for:
1- Food
2- Space
3- Breeding partners

Question 7

Explain how light is an abiotic factor

Answer 7

Photosynthesis = success of plant species

Question 8

Explain how temperature is an abiotic factor

Answer 8

• Enzymes = faster/slower metabolic reactions

- Migration + hibernation

Question 9

Explain how water availability is an abiotic factor

Answer 9

Lack of water = water stress = death

Question 10

Explain how oxygen availability is an abiotic factor

Answer 10

Aerobic respiration

Question 11

Explain how soil factors are an abiotic factor

Answer 11

Different soil types have different sized particles which affects the organisms that can live there

Question 12

What is biomass?

Answer 12

The mass of living material present in a particular place or in particular organisms

Question 13

What is the easiest way of measuring biomass?

Answer 13

• Calculate dry mass

Question 14

How do you calculate dry mass?

Answer 14

Discount water content by:

• Killing organism
• Place in oven at 80°C

Question 15

Why might dry mass not be representative?

Answer 15

Only a small sample is taken to minimise destruction of organisms

Question 16

What are the units of biomass?

Answer 16

• Land = g m -2

- Water = g k -3

Question 17

What is the energy available at each trophic level measured in?

Answer 17

kJ m-2 yr-1

Question 18

What is ecological efficiency?

Answer 18

The efficiency with which biomass of energy is transferred from one trophic level to the next

Question 19

Why do producers only convert 1-3% of sunlight into biomass?

Answer 19

• Approximately 90% is reflected
• Other factors may limit PHS
• Some energy is lost for PHS reactions

Question 20

What is gross production?

Answer 20

The total solar energy that plants convert to organic matter

Question 21

How do you calculate net production?

Answer 21

Gross production - respiratory losses

Question 22

Why do consumers convert a maximum of 10% biomass from food to their own organic tissue?

Answer 22

• Not all of the biomass is eaten
• Some energy is transferred as heat
• Some parts of an organism are indigestible
• Some energy is lost in excretory materials

Question 23

How do you calculate ecological efficiency?

Answer 23

Energy after transfer/Energy before transfer x 100

Question 24

What can humans do to maximise ecological efficiency?

Answer 24

• Remove predators
• Remove competition
• Provide food
• Provide optimum abiotic conditions

Question 25

Describe the nitrogen cycle

Answer 25

- Nitrogen is fixed into ammonia by Rhizobium (roots) & Azotobacter (soil) - Also by Haber process & lightning - Ammonia undergoes nitrification into nitrites, by Nitrosomonas - Nitrites undergo nitrification into nitrates, by Nitrobacter - Nitrates undergo denitrification into nitrogen gas - Or nitrates are taken up by plants & then to animals so plant & animal protein undergoes ammonification by decomposers into ammonia

Question 26

Describe the carbon cycle

Answer 26

- CO2 photosynthesised into plant material - Carbon is transferred to animals via feeding - CO2 is returned to atmosphere via respiration - When animals/plant die, the carbon is released by decomposition back to atmosphere - If decomposition is prevented, carbon forms fossil fuels which, when combusted, release CO2 into atmosphere

Question 27

What is primary succession?

Answer 27

Succession that occurs on newly formed land with no organic material

Question 28

Describe the first stage of primary succession

Answer 28

Pioneer community | - Pioneer species colonises inhospitable land

Question 29

Describe the second stage of primary succession

Answer 29

Intermediate community - Weathering of bare rock produces basis of a soil - Pioneer species decompose & release humus - Soil can now support secondary colonisers - Secondary colonisers decompose & release organic material so the soil can now support tertiary colonisers etc

Question 30

What are 2 adaptations of the pioneer species?

Answer 30

- Ability to photosynthesise | - Tolerant to extreme environments

Question 31

Describe the third stage of primary succession

Answer 31

Climax community - Optimum conditions - Environment rarely changes - 1 or 2 species become dominant

Question 32

What is plagioclimax?

Answer 32

The final stage of succession, when humans interrupt it